In May
1932S.V.Ilyushin
(at the time - head of the
TsKB) made
N.N.Polikarpov
as a deputy of
P.O.Sukhoj
- head of brigade 3, working on advanced I-14 monoplane fighter.
S.V.Ilyushin
suggested more conservative 'backup' sesquiplane I-14B (with retractable gear) and I-14A (with
fixed landing gear).
N.N.Polikarpov
accepted responsibility for the second one, which gradually evolved into the I-15 design.

Mock-ups of the I-14
(P.O.Sukhoj) and I-14A
(N.N.Polikarpov)
were presented in November
1932. On December 8 both
projects were approved, I-14 as a high speed interceptor and I-15 as a highly
maneuverable dogfighter. At the time
N.N.Polikarpov
got his separate design brigade.

I-15 was a small biplane fighter, development of the
I-5 and I-6 with
improved airdynamic. The most distinctive features were gulled upper wing and very clean fixed landing gear, often
covered with fairing. Roots of the upper wing were included into fuselage structure. Upper wing shape improved pilot
view and reduced drag.

Front section of the fuselage from engine to cockpit was covered with duralumin sheets, the rest of aircraft - with
fabric. Wheels were equipped with disk brakes. First aircraft was equipped by imported 630/715hp high altitude
Wright-Cyclone SGR-1820 F-3 engine. Armament included pair of synchronized
PV-1 machineguns and 40kg of bombs (overload). Interestingly, the tail of the first TsKB-3
carried same letters VT as the VT-11
prototype of the I-5.

Flight tests were performed in October-November
1933 by
V.P.Chkalov. The second prototype - on skis - was flown in December. During continuous
dive one of skis was lost, and aircraft turned over during landing.

Series production of I-15 started.

Early series were powered by Wright-Cyclone engine. Planned production
of its license version M-25 was delayed, and during 1934-36 few hundred of I-15
were equipped with M-22. Interestingly, low altitude performance did not suffer
despite less powerful engine was used. Since
1936
all production aircraft had
M-25 engine, demonstrating improved performance at high altitudes. Production aircraft
carried four PV-1 machineguns or (in
1938) pair of
12.7mmBS heavy machineguns.

Stripped version of the I-15 was used in
1935
by V.K.Kokkinaki to set the World altitude record (14,575m). Series of trials were performed in
1937
with pressurized cockpit. They had no value for series I-15 (due to ceiling), but those were first successful tests of
pressurized cockpits on Soviet fighters.

Gull-wing caused heated debates among specialists and pilots, despite
the I-15 was superior compared with other contemporary fighters. As a result
N.N.Polikarpov
had to convert design back to conventional wing. This conversion forced production delay in
1936
(only 12 I-15 rolled out). But while large series with straight wing started in
1937
(picture below), extensive airdynamic tests at
TsAGI
proved advantage of the gull wing at high speeds, and in
1938
I-15 production continued with (modified) gull wing.

Straight-winged I-15 of
1937
series (104k!) from 'Aviatsia i Vremia' ('Aviation and Time') magazine, courtesy of
Sergey Andreev

The I-15 was used in combat in Spain and proved to be one of the best
fighter biplanes of its time. Performance was high enough to force pilots of early Bf-109
to avoid close combat with more agile and well-armed 'Chato'. But biplane era was already
fading, and in
1939
during clashes with Japanese I-15 was already obsolete.

I-15 deserves special honor from American military pilots. It was flown
by ace of Spanish War Frank G. Tinker, who became the first American to shot down Messerschmitt Bf-109...